Voltage transformer

ABSTRACT

A voltage transformer comprising a hollow support insulator within which is arranged a main insulator and associated with this, a magnetic circuit, at least one primary winding and at least one secondary winding, together with necessary conductors. The main insulator is of tubular form and made up of a number of metal foil tube elements located inside each other in such a manner as to overlap each other partially but not completely, with insulator elements of tubular form arranged between them. A first winding (either a primary or a secondary winding) is located around the main insulator and a second winding (either a secondary or a primary winding) is located inside the main insulator approximately opposite to said first winding. The magnetic circuit comprises two separate core sections, one of which extends from the surface of the main insulator, enclosing the first winding, at least approximately to the other end of the main insulator and the other of which extends from the surface of the main insulator, enclosing from inside the second winding, to the said other end of the main insulator where it meets the other end of the first core section.

Panu

[451 Feb. 12,1974

l 54 l VOLTAGE TRANSFORMER [75] Inventor: Vaino Tuure Kalevi Panu,Vaasa,

Finland [73] Assignee: Oy Stromberg AB, Vassa, Finland 22 Filed: Mar.20,1973

[21] Appl. N0.: 343,147

[58] Field of Search. 336/69, 70,84, 173, 174, 175,

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 904,761 11/1945France 336/174 726,194 10/1942 Germany 336/70 839,662 4/1939 France336/70 Primary ExaminerThomas .l. Kozma Attorney, Agent, or Firm-Young &Thompson [57] ABSTRACT A voltage transformer comprising a hollow supportinsulator within which is arranged a main insulator and associated withthis, a magnetic circuit, at least one primary winding and at least onesecondary winding, together with necessary conductors. The maininsulator is of tubular form and made up of a number of metal foil tubeelements located inside each other in such a manner as to overlap eachother partially but not completely, with insulator elements of tubularform arranged between them. A first winding (either a primary or asecondary winding) is located around the main insulator and a secondwinding (either a secondary or a primary winding) is located inside themain insulator approximately opposite to said first winding. Themagnetic circuit comprises two separate core sections, one of whichextends from the surface of the main insulator, enclosing the firstwinding, at least approximately to the other end of the main insulatorand the other of which extends from the surface of the main insulator,enclosing from inside the second winding, to the said other end of themain insulator where it meets the other end ofthe first core section.

14 Claims, 1 Drawing Figure Bi w PATENTEDFEBI2I974 VOLTAGE TRANSFORMERThis invention concerns a voltage transformer comprising a hollowsupport insulator within which is arranged a main insulator, a magneticcircuit associated with this, at least one primary winding and at leastone secondary winding, togetherwith necessary conductors.

ln pin core type voltage transformers the core con sists of aferromagnetic pin onto which the secondary winding is wound in the formof a long cylinder. The main insulation which is tube shaped is fittedover the secondary winding and carries the cylindrical primary winding.The magnetic circuit is closed across an air gap which means that theequivalent air gap of the magnetic circuit is relatively long. A largeiron crosssectional area and/or a large'number of winding turns arenecessary in order to obtain sufficiently high offload inductance. Thedimensions of the active parts of the transformer and therefore thematerial costs are high. The potential, during high speed voltagevariation phenomena, is distributed in a non-linear fashion in thelongitudinal direction of the primary winding owing to the large earthcapacitance, necessitating more insulation between the upper turns thanelsewhere in the winding.

The purpose of the invention is to eliminate these aforementioneddisadvantages.

The voltage transformer in accordance with the invention is mainlycharacterised in that the main insulator is of tubular form and made upof a number of metal foil tube elements located inside each other insuch a manner as to overlap each other partially but not completely,with insulator elements of tubular form fitted between them, in that atleast one first winding (either a primary or a secondary winding) islocated around the main insulator and at least one second winding(either a secondary or a primary winding) is located inside the maininsulator at least approximately opposite to the said first winding andin. that the magnetic circuit comprises two separate core sections, oneof which extends from the surface of the main insulator, enclosing thefirst winding, at least approximately to the other end of the maininsulator, and the other of which extends from the surface of the maininsulator, enclosing from inside the second winding, to the said otherend of the main insulator where it meets the other end of the first coresection.

The invention is described in more detail in the following withreference to the attached drawing. The drawing shows a cross-section ofone embodiment of the voltage transformer in accordance with theinvention.

The main insulator tube 1 of the transformer has a length 2H-l-H, whereH a the shortest permissible distance over which the voltage can bedistributed in the axial direction of the support insulator, and H theheight of the yoke through which the insulator tube passes. The maininsulator tube 1 is made up of cylinders of metal foil 11 of mutuallyequal length H+H' located inside each other and thin insulatingcylinders 12 of mutually equal thickness and greater length than thefoil cylinders 11, lcoated between the aforementioned metal foilcylinders. At one end of the main insulator tube 1, the ends of themetal foil cylinders are located at a distance H/m further away from themidpoint of the main insulator tube 1 and correspondingly at the otherend, the same distance nearer to the midpoint of the main insulator tube1 than the end of the next metal foil cylinder inside, where m thenumber of insulating cylinders 12.

A primary winding 5 is wound coaxially to the main insulator tube 1 overa distance H, beginning from one end of the main insulator tube 1, insuch a manner that the ends of the metal foil cylinders 11 are at thesame level as the primary winding 5, and on the same side of the maininsulator tube 1 as the primary winding 5 in the radial direction.

A secondary winding 4 is wound, level with the primary winding 5 in theaxial direction, but, in the radial direction, on the opposite side ofthe main insulator tube 1. One half 2,2,2" of the magnetic circuit 2,3,6

extends in one continuous ferromagnetic section from the middle of themain insulatortube 1, from the surface of the tube, around the secondarywinding 4 and I the bottom edge of the main insulator tube 1 to the endof the primary winding 5 which is at earth potential, and is thuscompletely at approximately earth potential.

The other half 3,6 of the magnetic circuit 2,3,6 comprises a magneticcolumn 6, electrically insulating in the longitudinal direction, whichextends from the lower end 14 of the primary winding 5 which is at earthpotential, to the high voltage end, and a yoke 3 which extends from thehigh voltage end 15 of the primary winding 5 to the surface of themiddle section of the main insulator tube 1 on the same level, but atthe other side of tube 1 in a radial direction, than the half 2 of themagnetic circuit which is at earth potential. A magnetic circuit whichencloses the primary and secondary windings 5, 4 and that section of themain insulator tube 1 located between them is thus formed, the circuitbeing broken by the main insulator tube with an air gap whose length isthe insulation thickness.

Core 2,3,6 together with windings 5, 4 and main insulator tube 1 islocated within a hollow support insulator 7 in such a way that the axisof the main insulator tube 1 is parallel to the axisof the supportinsulator 7 and that the end of the main insulator tube 1 where all theends of the metal foil cylinders 11 are on the outer surface iscompletely within the support insulator 7.

All the active parts of the transformer are thus located within thehollow support insulator 7. The ferromagnetic inner column 2 which is atearth potential is provided with flanged ends 2" and functions as a reelbody for the secondary winding 4 which has the form of a cylinder. Themain insulator tube 1 is wound over the cylinder made up of theferromagnetic inner column 2 and the secondary winding 4 in such amanner that the lower end of the innermost metal foil cylinder is on alevel with the lower end of the secondary winding 4 and the end of theoutermost metal foil layer 11 is opposite to the upper end of thesecondary winding 4. The lower end of the main insulating tube 1 istherefore composed of filler insulation 13 in order that the primarywinding 5 can be wound onto a base having the form of a tube of constantdiameter. The turns of the primary winding 5 are uniformly distributedover the distance H and the distribution of potential is linear.

Over the primary winding 5, is located'a cylindrically shaped magnetictube 6 which is electrically insulating in the longitudinal direction,the upper end being galvanically connected (point 16) to the upper end15 of the primary winding 5 and the lower end being at earth potentialthrough conductors 10,21,17. The ferromagnetic yoke 3 which is wholly atthe potential of the upper end of the primary winding 5 is locatedbetween the upper end of the electrically insulating tube 6 and theouter surface of the middle section of the main insulating tube 1. Themain insulating tube 1 passes through the yoke 3, thus breaking themagnetic circuit 2,3,6 with an air gap whose length is the insulatingthickness. The effect of the air gap on the characteristics of themagnetic circuit 2,3,6 can be decreased by increasing the height H ofthe yoke.

Differing from the embodiment described above, but within the scope ofthe invention, the positions of the primary and secondary windings canbe interchanged, said electrically insulating magnetic tube 6 then beinglocated inside the main insulator 1.

It is not necessary for the core section 3,6 to have the shape of acoaxial ring, but it can also have the form of, e.g., a column. The coresection 2 could be located around the main insulator and the firstwinding. The core section 2" need not be provided with flanges, and itcould also extend inwards (in the case where the primary winding islocated inside the main insulator).

What we claim is:

1. A voltage transformer comprising:

a. a hollow support insulator;

b. a main insulator having tubular form and being arranged within saidsupport insulator and being made up of a number of metal foil tubeelements located inside each other in such a manner as to overlap eachother at least partially, and of a number of tubular insulator elementsarranged between said metal foil tube elements;

c. at least one first winding arranged coaxially around said maininsulator;

d. at least one second winding arranged coaxially inside said maininsulator at least approximately opposite to said first winding;

e. a magnetic circuit comprising a first and a second core section, saidfirst core section extending from the outer surface of the maininsulator, enclosing from outside said first winding, at leastapproximately to one end of said main insulator, said second coresection extending from the inner surface of said main insulator,enclosing from inside said second winding, to said end of said maininsulator where it meets one end of said first core section; and

f. a number of conductors interconnecting the different parts of thetransformer.

2. A voltage transformer as claimed in claim 1, wherein the metal foiltube elements are of mutually equal length 3. A voltage transformer asclaimed in claim 1,

wherein the insulating elements of tubular form are of mutually equallength and are longer than the metal foil tube elements.

4. A voltage transformer as claimed in claim 1, wherein the metal foiltube elements and the insulating elements are of cylindrical shape.

5. A voltage transformer as claimed in claim 1, wherein the metal foiltube elements are in mutually equally spaced steps and the insulatingelements are also in mutually equally spaced steps.

6. A voltage transformer as claimed in claim 1, wherein the insulatingelements are of mutually equal thickness.

7. A voltage transformer as claimed in claim 1, wherein the ends of thetube elements overlap in those parts of the main insulator which arelocated outside the core in the axial direction of the main insulator.

8. A voltage transformer as claimed in claim 1, wherein the firstwinding and the second winding are in the shape of cylindrical ringslocated one inside the other.

9. A voltage transformer as claimed in claim 1, wherein the inner partof the second core section is of cylindrical shape and is provided witha groove on which the second winding is wound.

10. Avoltage transformer as claimed in claim 1,

wherein the first core section has the shape of a cylindrical ring andis provided with an inside groove for the first winding.

11. A voltage transformer as claimed in claim 1, wherein the axialdimension of the core sections is greater than that of the windings.

12. A voltage transformer as claimed in claim 1, wherein the first coresection comprises a yoke designed to fit onto the main insulator and acolumn connected to it, which is located at least approximately oppositeto the first winding in the axial direction and is electricallyinsulating in the axial direction.

13. A voltage transformer as claimed in claim 1, wherein the primarywinding comprises several coils located above each other in the axialdirection.

14. A voltage transformer as claimed in claim 1, wherein the first coresection surrounds the main insulator tube and the first winding as acoaxial ring in such a manner that one of its ends is at leastapproximately opposite to one end of the main insulator tube in theaxial direction, and the second core section includes an inner partdesigned to fit at least approximately against the inner surface of theinsulator tube and the second winding, and an outer part ending at saidend of the main insulator tube and terminating outwards in a flange-typestructure.

1. A voltage transformer comprising: a. a hollow support insulator; b. amain insulator having tubular form and being arranged within saidsupport insulator and being made up of a number of metal foil tubeelements located inside each other in such a manner as to overlap eachother at least partially, and of a number of tubular insulator elementsarranged between said metal foil tube elements; c. at least one firstwinding arranged coaxially around said main insulator; d. at least onesecond winding arranged coaxially inside said main insulator at leastapproximately opposite to said first winding; e. a magnetic circuitcomprising a first and a second core section, said first core sectionextending from the outer surface of the main insulator, enclosing fromoutside said first winding, at least approximately to one end of saidmain insulator, said second core section extending from the innersurface of said main insulator, enclosing from inside said secondwinding, to said end of said main insulator where it meets one end ofsaid first core section; and f. a number of conductors interconnectingthe different parts of the transformer.
 2. A voltage transformer asclaimed in claim 1, wherein the metal foil tube elements are of mutuallyequal length.
 3. A voltage transformer as claimed in claim 1, whereinthe insulating elements of tubular form are of mutually equal length andare longer than the metal foil tube elements.
 4. A voltage transformeras claimed in claim 1, wherein the metal foil tube elements and theinsulating elements are of cylindrical shape.
 5. A voltage transformeras claimed in claim 1, wherein the metal foil tube elements are inmutually equally spaced steps and the insulating elements are also inmutually equally spaced steps.
 6. A voltage transformer as claimed inclaim 1, wherein the insulating elements are of mutually equalthickness.
 7. A voltage transformer as claimed in claim 1, wherein theends of the tube elements overlap in those parts of the main insulatorwhich are located outside the core in the axial direction of the maininsulator.
 8. A voltage transformer as claimed in claim 1, wherein thefirst winding aNd the second winding are in the shape of cylindricalrings located one inside the other.
 9. A voltage transformer as claimedin claim 1, wherein the inner part of the second core section is ofcylindrical shape and is provided with a groove on which the secondwinding is wound.
 10. A voltage transformer as claimed in claim 1,wherein the first core section has the shape of a cylindrical ring andis provided with an inside groove for the first winding.
 11. A voltagetransformer as claimed in claim 1, wherein the axial dimension of thecore sections is greater than that of the windings.
 12. A voltagetransformer as claimed in claim 1, wherein the first core sectioncomprises a yoke designed to fit onto the main insulator and a columnconnected to it, which is located at least approximately opposite to thefirst winding in the axial direction and is electrically insulating inthe axial direction.
 13. A voltage transformer as claimed in claim 1,wherein the primary winding comprises several coils located above eachother in the axial direction.
 14. A voltage transformer as claimed inclaim 1, wherein the first core section surrounds the main insulatortube and the first winding as a coaxial ring in such a manner that oneof its ends is at least approximately opposite to one end of the maininsulator tube in the axial direction, and the second core sectionincludes an inner part designed to fit at least approximately againstthe inner surface of the insulator tube and the second winding, and anouter part ending at said end of the main insulator tube and terminatingoutwards in a flange-type structure.